Biological molecules

• Water

  Polar due to unevenly distributed charges, H-bonds between O and H atoms as positive and negative regions interact
• Proteins

  • Made up of one or more large polymers, creating a macromolecule
  • Primary structure = order of amino acids in polypeptide chain
  • Secondary structure = parts of protein molecule bend into α helix or β pleated sheet, held by H-bonds
  • Tertiary structure = secondary structure bent and folded into 3D shape, held by hydrophobic/hydrophilic interactions, H-bonds, ionic bonds, disulfide bonds
  • Quaternary structure = protein made of more than one polypeptide chain
• Conjugated protein

  Protein with a non-protein prosthetic group attached, e.g. haemoglobin with haem group
• Globular proteins

  • Polypeptide chains rolled up into spherical shape, relatively unstable structure, soluble, carry out metabolic functions
• Fibrous proteins

  • Long twisted strands linked together, stable structure, insoluble in water, provide structural function, e.g. collagen, keratin
• Isomers

  Molecules with same molecular structure but different spatial structure, e.g. α and β glucose
• Disaccharide formation

  Two monosaccharides joined by glycosidic bond in condensation reaction, e.g. maltose, lactose, sucrose
• Condensation

  Joining two molecules by removing water
• Hydrolysis

  Splitting molecules by adding water
• Lipids

  • Macromolecules, not polymers, non-polar, insoluble in water but soluble in organic solvents, hydrophobic
• Triglycerides

  Formed by condensation of 1 glycerol and 3 fatty acids, forming ester bonds
• Saturated fatty acids

  • Hydrocarbon chain has only single bonds between carbons
• Unsaturated fatty acids

  • Hydrocarbon chain has at least one double bond between carbons
• Phospholipids

  Made of glycerol, 2 fatty acid chains, and a phosphate group, form bilayer membrane structure
• Cholesterol

  Sterol with 4 carbon rings and a hydroxyl group, embedded in cell membranes to regulate fluidity
• Triglyceride structure


  • Can transfer energy due to the large ratio of energy-storing carbon-hydrogen bonds compared to the number of carbon atoms
  • Can act as a metabolic water source due to the high ratio of hydrogen to oxygen atoms
  • Are large, hydrophobic molecules that are insoluble in water, so they do not affect water potential and osmosis
  • Are relatively low in mass, so a lot can be stored in an animal without increasing mass and preventing movement
• Phospholipid


  Has a hydrophilic 'head' that can attract water as it is charged, and a hydrophobic 'tail' that repels water but mixes with fats
• The phosphate in a phospholipid is charged, so it repels other fats
• The fatty acid chain in a phospholipid is not charged